534 On the Hot-wire Anemometer. 



There is seen to be very close agreement between the 

 values for the ratio in the cases of carbon dioxide, nitrogen, 

 and air as determined experimentally by the flow method, 

 and those calculated from Winkelmann's results at 0° C. 

 The values do not agree with the calculated values of the 

 ratios at 350° C. These results are explainable on the as- 

 sumption of the existence of a very thin layer of stagnant 

 gas surrounding the heated wire, the temperature gradient 

 in such layer being great. This cylinder of gas then func- 

 tions as the source of heat whence heat is directly transferred 

 to the gas, and its effective temperature need only be slightly 

 in excess of that of the gas-stream. In the case of oxygen 

 and air, while the agreement between the experimentally 

 determined values is not so close as in the other two cases, 

 there is, however, fair agreement. The difference of 10 per 

 cent, may be possibly attributable to the use of an uncertain 

 value of the specific heat for oxygen at constant A^olume. 

 The value employed has been deduced from Regnault's 

 value of the specific heat at constant volume, taking 

 7 = 1-40. 



The same method for the comparison of the thermal con- 

 ductivities of the gases employed with the glass-covered 

 anemometer wire cannot be used, as the temperature of the 

 wire with zero flow when immersed in coal-gas etc. and in 

 air was not sufficiently constant in the case of the various 

 gases, and as, moreover, the observations with hydrogen etc. 

 m this case were not carried out at sufficiently high velocities 

 to render the theory valid. 



This research was carried out at the Physical Laboratory 

 of the South Metropolitan Gas Company, and the author 

 desires to express his sincerest thanks to Dr. Charles 

 Carpenter, C.B.E., for the ready provision of the facilities 

 necessary for carrying out the work, and for permission 

 to publish the same. 



Physical Laboratoiy, 



South Metropolitan Gas Co., 

 709 Old Kent Boad, S.E. 

 Dec. 18th, 1919. 



